For various reasons, operators may want to cut into the side of casing in an existing wellbore so a new sidetracked or lateral wellbore can be drilled. For example, the formation adjacent the original wellbore may become depleted or damaged, or a tool or pipe may have become stuck and may have blocked further use of the original wellbore. For whatever reason, the sidetracked wellbore can be drilled and then lined with pipe for additional operational uses.
As illustrated in FIG. 1A, a whipstock 20 according to the prior art can be used for diverting a milling tool to create a sidetracked wellbore 40. Operators run the whipstock 20 down the original wellbore's casing 12 to the desired location. The whipstock 20 has a wedge-shaped member or whip 22 with a concave face 24 that can steer a mill or cutter 42 to the side of the casing 12 where a window will be formed. Whipstocks and their use are known, and an example is shown in U.S. Pat. No. 6,464,002, which is incorporated by reference herein in its entirety.
The whipstock 20 may be run in by itself on a setting tool, and the mill 42 can be run in after the whipstock 20 has been set. Alternatively, to save a trip, the whipstock 20 can be run in with the mill 42 temporarily attached to its upper edge. In either case, the whipstock 20 uses an anchor 30 on its end so the whipstock 20 can be anchored in the wellbore 10 at the desired location. The anchor 30 sets in the casing 12 and keeps the whipstock 20 in place to resist the downward force placed upon it as the mill 42 moves along its length through the wall of the casing 12.
Various types of anchors can be used with the whipstock 20, and the anchors can be set mechanically or hydraulically. Mechanically-set anchors require a compressive force to shear a pin so the anchor can be set. These mechanical anchors work well when the anchor is to be set at the bottom of a wellbore or when there is some type of restriction that has been placed in the wellbore, like a bridge plug, against which the anchor can rest. In those instances, the stationary surface available in the wellbore allows operators to generate the compressive force needed to set the mechanical anchor.
In other instances, the anchor may be positioned at some point along the wellbore where there is no surface against which to create a compressive force. In these instances, the anchor can be set with pressurized fluid and requires a hydraulic mechanism.
One particular type of hydraulically-set anchor 30 for the whipstock 20 is shown in FIG. 1A. This anchor 30 and whipstock 20 can be similar to what is disclosed in U.S. Pat. No. 5,154,231. The hydraulically-set anchor 30 is attached to the end of the whipstock's whip 22. A running tool (i.e., string or the mill 42) detachably secures to the whip 22 for deployment and possible retrieval. In addition to these components, the whipstock 20 can have a locator sub with outwardly biased locator dogs (not shown) to engage in a prior milled positioning window (if formed) in the casing 12.
With the whipstock 20 positioned in the wellbore 10, the anchor 30 can be set to secure the whip 22 for the milling process. The running string (or mill 42 when used for run-in) can supply hydraulic fluid through a line to communicate with the anchor 30, pressurize the anchor's mechanism, and set the anchor 30 in the casing 12. For example, hydraulic fluid pressure is supplied to the anchor 30 and can expand slip elements 34 on the anchor 30 outwardly to engage the casing 12 and set the anchor 30. With the anchor 30 set, the mill 42 can then mill the wellbore diversion through the wall of the casing 12. After milling, the whipstock 20 may or may not be retrievable depending on its design.
Sometimes, the anchor 30 has a packer 32 that can isolate the lower portion of the wellbore 10 when set. Other times, isolation may not be necessary. Either way, being able to operate the packer 32 on the anchor 30 for the whipstock 20 offers some unique challenges.
One particular type of anchor 30 available in the art is shown in FIG. 1B and is disclosed in U.S. Pat. No. 7,963,341, which is incorporated herein by reference in its entirety. This anchor 30 has first and second inclined bodies 31a-b with a cavity 33c formed between their inclined surfaces 33a-b. The bodies 31a-b can slidably move relative to each other along a portion of their inclined surfaces 33a-b to increase an outer diameter of the anchor 30 in a set position. A biasing member 35 disposed in the cavity 33c can move the anchor 30 from a run-in position to the set position with the increased outer diameter. A triggering mechanism 37 initiates movement of at least one of the bodies 31a-b to the set position. The triggering mechanism 37 includes a shearable connection and a releasable locking connection that releases the biasing member 35.
Although existing whipstocks 20 and anchors 30 used in the art are effective. Operators are continually seeking new tools that can meet the new challenges experienced in the oil and gas industry around the world. For these reasons, the subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.